Take them places. Show them stuff. Talk about the places and the stuff. Let your baby see you living your life. That's what Maria said was the best way for little babies to learn.
As for actual activities:
Get a basket, put various things in the basket, change out the things after a week or so.
Go outside with a big bowl of water. Include a cup.
Pour flour on a tray on a floor that can be swept/vacuumed easily. Include a spoon.
With extra supervision, provide bowls of various textures of things. E.g. dried beans, couscous, rice.